BS ISO 7781-2017 pdf free download.Styrene-butadiene rubber, raw — Determination of soap and organic-acid content
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.
5.1 Ethanol-toluene azeotrope (ETA).
Mix seven volumes of absolute ethanol with three volumes of toluene. Alternatively, mix seven volumes of commercial-grade ethanol with three volumes of toluene, and boil the mixture with anhydrous calcium oxide (quicklime) under reflux for 4 h. Cool to room temperature and decant through No. 42
filter paper.
5.2 Ethanol-toluene-water mixture.
Mix 95 cm 3 of ETA (5.1) and 5 cm 3 of water.
5.3 Sodium hydroxide solution, c(NaOH) = 0,1 mol/dm 3 , accurately standardized.
5.4 Thymol blue indicator.
Dissolve 0,06 g of thymol blue in 6,45 cm 3 of 0,02 mol/dm 3 sodium hydroxide solution and dilute to 50 cm 3 with water.
5.5 Hydrochloric acid, c(HCl) = 0,05 mol/dm 3 , accurately standardized.
6 Apparatus
Use ordinary laboratory apparatus and the following.
6.1 Balance, accurate to 1 mg.
6.2 Hotplate.
6.3 Wide-mouthed? conical? flask, of capacity 400 cm 3 to 500 cm 3 .
6.4 Volumetric? flask, of capacity 250 cm 3 , complying with the requirements of ISO 1042 .
6.5 Reflux? condenser, complying with the requirements of ISO 4799 .
6.6 Conical? flask, of capacity 250 cm 3 .
NOTE Alternatively, a Soxhlet extractor can be used instead of a reflux condenser and a conical flask.
6.7 Burette, of capacity 25 cm 3 , complying with the requirements of ISO 385 .
6.8 Pipette, of capacity 100 cm 3 , complying with the requirements of ISO 648 .
6.9 Pipette, of capacity 2 cm 3 , complying with the requirements of ISO 648 .
6.10 Magnetic stirrer, with a polytetrafluoroethylene-coated stirrer bar.
6.11 Automatic potentiometric titrator, including an electrode which is applicable to test the pH of organic solution.
7 Sampling and sample preparation
Sheet out 2 g to 6 g of rubber, selected and prepared in accordance with ISO 1795 . Cut into pieces no larger than 2 mm × 2 mm or strips no longer than 10 mm and no wider than 5 mm. Weigh a test portion of approximately 2 g to the nearest 0,001 g.
8 Procedure
8.1 Preparation of the test solution
Place a circular filter paper in the bottom of the wide-mouthed conical flask (6.3), and add 100 cm 3 of ETA extraction solvent (5.1) for all rubbers except alum-coagulated rubbers. For alum-coagulated rubbers, use an ethanol-toluene-water mixture (5.2).
Introduce the strips of rubber separately into the flask, swirling after each addition so that the strips are thoroughly wetted with solvent and sticking is minimized.
Fit the reflux condenser (6.5) to the flask and boil the solvent very gently under reflux for 1 h.
Transfer the extract to the volumetric flask (6.4), and treat the rubber with a second 100 cm 3 portion of extraction solvent under reflux for 1 h. Add this extract also to the volumetric flask. Rinse the strips with three successive 10 cm 3 portions of extraction solvent, add these washings to the volumetric flask and, after cooling to room temperature, adjust the final volume to 250 cm 3 with appropriate extraction solvent.
Alternatively, the weighed strips of sample can be wrapped in filter paper and placed in a Soxhlet extractor (see Note to 6.6) and extracted with an ETA (5.1) or ethanol-toluene-water mixture (5.2) under reflux for a minimum of 4 h.
8.2 Method A — Titration method using indicator reagent
8.2.1 Procedure for determination of soap content
After thorough mixing, pipette 100 cm 3 of the diluted extract into the 250 cm 3 conical flask (6.6), add six drops of thymol blue indicator (5.4) and titrate the solution with hydrochloric acid solution (5.5) to the first colour change (V 1 ).
Carry out a blank titration on 100 cm 3 of extraction solvent taken from the same stock as was used for the test portion and using the same indicator as used for titration of the test portion (V 2 ).
8.2.2 Procedure for determination of organic-acid content
Proceed exactly as in 8.2.1, but titrate the aliquot portion with sodium hydroxide solution (5.3), again using thymol blue indicator (5.4) (V 3 ).
Carry out a blank titration on 100 cm 3 of extraction solvent using the same method (V 4 ).
8.3 Method B — Titration method using automatic potentiometric titrator
8.3.1 Procedure for determination of soap content
Turn on the automatic potentiometric titrator (6.11), and allow the electronic circuit to stabilize.
Pipette 100 cm 3 of the test solution into a 250 cm 3 beaker containing a stirrer bar, then place the beaker on the magnetic stirrer (6.10). Insert the electrode into the test solution in the beaker.
While stirring, titrate the test solution with hydrochloric acid solution (5.5). Record the volume of hydrochloric acid solution used at the equivalence point that is given as the inflection point of the
titration curve (V 1 ).
NOTE The x-axis value of the inflection point of the titration curve is shown as the x-axis value of maximal value point of the derivative of the titration curve. This x-axis value is the volume of hydrochloric acid solution used at the equivalence point.
Carry out a blank titration on 100 cm 3 of extraction solvent using the same method (V 2 ).BS ISO 7781 pdf download.